REACTION OF AMINOCARBENE COMPLEXES OF CHROMIUM WITH ALKYNES .1. FORMATION AND REARRANGEMENT OF KETENE AND NITROGEN YLIDE COMPLEXES

The title reactions of chromium-containing carbene complexes (CO)5Cr=C(R1)N(R2R3) (R1 = H, Me, Ph; R2 = Me; R3 = Me, C3H5, CH2C3H5; R2R3 = (CH2)5) 8 and (CO)5Cr=C[(CH2)3C=CPh]N(R1R2) (R1 = R2 = Me; R1R2 = (CH2)5; R1R2 = (CH2)4) 9, bearing alkyl groups of low migratory aptitude on nitrogen, have been examined. In contrast to complexes in which nitrogen bears either an alkyl and an allyl or a benzyl group or is part of a strained cycle, which give heterocycles upon alkyne/CO insertions followed by nitrogen-to-carbon migrations (e.g., 1 --> 7), complexes 8 and 9 lead to stable nitrogen ylides, which could be fully characterized by X-ray crystallography in the case of 8a and 9a. Moreover, in the case of complexes of the general structure 9, ketene precursors of the ylides could either be detected (R1 = Me; R2 = CH2Ph) or isolated and characterized (R2R3 = (CH2)5). The new ylide complexes undergo, upon moderate heating, Stevens-type rearrangements to the expected heterocyclic compounds as a result of nitrogen-to-carbon migrations of various alkyl groups, and upon treatment with dimethyldioxirane, they undergo oxidation to lactone complexes.